Conventionally, a processing object such as a semiconductor wafer is diced, i.e., cut and separated, by using a laser beam. This laser dicing method is disclosed in, for example, Japanese Patent No. 3408805. In this method, the laser beam is irradiated on the processing object such as a wafer to focus on the inside of the object. Thus, a reforming portion is formed in the inside of the object by multiple photon absorption effect of the laser beam. The reforming portion includes a crack, a melting region, or a region, of which a refractive index is changed. The reforming portion provides a starting point of dicing, which is formed along with a dicing line of the object and disposed inside of the object apart from the surface of the object by a predetermined distance. The laser beam is irradiated on the surface of the object. The object is diced from the starting point.
Further, another technique is disclosed in, for example, JP-A-2002-205180. In this technique, a laser beam is irradiated on a processing object to focus on the inside of the object. A reforming portion is formed in the inside of the object along with a cutting line of the object. Further, the focus point of the laser beam in an incident direction of the laser beam is changed, so that multiple reforming portions are formed in the object along with the incident direction. In this technique, multiple starting points are formed. Accordingly, when the thickness of the object is large, the object can be diced easily.
Furthermore, another method for dicing an object is disclosed in, for example, JP-A-2005-1001. In the method, an extensible film is formed on one side of the object having a plate shape such as a substrate. The other side of the object is a laser beam incident surface. The laser beam is irradiated on the other side of the object to focus on the inside of the object. Thus, the reforming portion is formed so that the staring point of dicing is provided by the reforming portion along with a cutting line of the object. The starting point is disposed inside of the object from the laser beam incident surface by a predetermined distance. Then, the film is extended so that the object is separated and cut from the starting point. Thus, the object is divided into multiple chips. Since the film is extended when the object is diced, an appropriate tensile stress is applied around the starting point. Accordingly, the object is cut accurately with a comparative small force.
In the above methods, when the object is cut from the reforming portion as a starting point, or after the object is cut, a particle such as a small flake may be removed from a cutting surface, i.e., a dicing surface. The particle is formed from a component of the object. The particle generates a dust.
When the dust is attached to a semiconductor device formed on a chip, the semiconductor device may malfunction. Accordingly, a yielding ratio of the chip is reduced, and further, quality of the chip is also reduced.
For example, in a case where a monolithic IC as a semiconductor device is formed on the chip, when the particle is attached on the semiconductor element or a wiring in the monolithic IC, the particle may cause short-circuit.
In a case where a sensor such as a pressure sensor, an acceleration sensor and a supersonic sensor composed of a piezo-electric element and/or a capacitor or a micro-machine is formed on the chip by using a micro electro mechanical system method (i.e., MEMS method), when the particle is attached on a movable portion composing the sensor or the micro machine, the particle may prevent the movable portion from displacing. Thus, performance such as sensitivity in the sensor or the micro machine is reduced.
A dicing film, i.e., a dicing sheet, is disclosed in, for example, JP-A-2003-10986. The dicing film is bonded to a backside of a wafer as a processing object, which has a plate shape. The wafer provides a piezo element. The wafer is diced with a laser beam. Specifically, the wafer is cut and separated from a reforming portion as a starting point. When the wafer is divided into multiple piezo element chips, the dicing film protects the chips from spattering.
The dicing film is made of resin tape having adhesiveness. Specifically, one side of the dicing film has the adhesiveness so that the one side adheres to the wafer. In general, the periphery of the dicing film is held by a holder so that a certain tension is applied to the dicing film. Then, the holder with the dicing film is mounted on a base table, and the laser beam is irradiated on the wafer disposed on the dicing film. Thus, the reforming portion is formed in the wafer, and then, a pressure is applied to the wafer so that the wafer is pressed up from the backside of the dicing film. Thus, a crack is generated at the reforming portion as the starting point, and the crack becomes larger so that the wafer is cut and separated.
In this case, the particle removed from the dicing surface of the wafer is absorbed by an absorber. Thus, the dust, i.e., the particle from the dicing surface is removed from the wafer. The absorber absorbs the particle from the surface of the wafer. Accordingly, the air flow generated by the absorber for absorbing the particle directs to the upward of the wafer. Thus, the particle to be absorbed by the absorber may float above the wafer. Thus, the particle floating above the wafer is scattered in a wide range so that the particle spreads on the wafer or the chip. Thus, the yielding ratio of the chip and the quality of the chip are reduced.
Further, it is difficult to absorb the particle completely. Thus, residual particle may be adhered on the wafer or the chip, so that the yielding ratio of the chip and the quality of the chip are reduced. This particle is generated not only in a step of dicing the wafer but also in a step of laser abrasion.